White emitting light source and luminescent material

ABSTRACT

The invention relates to a white emitting light source with an improved luminescent material of the formula (AEN2/3)*b(MN)*c(SiN4/3)*d1CeO3/2*d2EuO*xSiO2*yAlO3/2 wherein AE is an alkaline earth metal chosen of the group of Ca, Mg, Sr and Ba or mixtures thereof and M is a trivalent element chosen of the group of Al, B, Ga, Sc with d1&gt;10*d2. In combination with a UV to blue light generating device this material leads to an improved light quality and stability, especially an improved temperature stability for a wide range of applications.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. application Ser. No. 14/320,988, filedJul. 1, 2014, which is a continuation of U.S. application Ser. No.13/917,673, filed Jun. 14, 2013, by Joerg Meyer et al., titled “WhiteEmitting Light Source and Luminescent Material, which is a continuationof U.S. application Ser. No. 12/595,660, filed Oct. 13, 2009, now U.S.Pat. No. 8,465,166, which is a National Stage Entry of PCT ApplicationNo. PCT/IB2008/051427, which is the International Application claimingpriority to EPO Application Serial No. 07106630.2. Each of U.S.application Ser. Nos. 14/320,988, 13/917,673, U.S. Pat. No. 8,465,166,PCT Application No. PCT/IB2008/051427, and EPO Application Serial No.07106630.2 is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention is directed to novel luminescent materials forlight emitting devices, especially to the field of novel luminescentmaterials for LEDs.

BACKGROUND OF THE INVENTION

For illumination purposes high CRI light sources are generallypreferred. White LEDs based on a single YAG:Ce luminescent colourconverter usually reach R_(a) values in the 70s with very bad colourrendering in the red spectral region. Therefore strong pressures existfor the development of efficient illumination grade white LEDs withexcellent colour rendering over the entire visible spectral region. Theobvious measure to improve colour rendering is the addition of a redemitting luminescent material (i.e. disclosed in the U.S. Pat. No.6,717,353). However fabrication of white LEDs becomes more cumbersomedue to the added degrees of freedom. Thus single phosphor options aredeemed to be favourable if not superior.

However, there is still the continuing need for novel emittingluminescent materials which are usable within a wide range ofapplications and especially allow the fabrication of white phosphorconverted LEDs (pcLEDs) with correlated colour temperature below 6000 K,optimized luminous efficiency and color rendering.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an illuminationsystem which is usable within a wide range of applications andespecially allows the fabrication of warm white pcLEDs with optimizedluminous efficiency and color rendering.

This object is solved by an illumination system according to claim 1 ofthe present invention. Accordingly, an illumination system is proposedcomprising at least one luminescent material essentially of thecompositiona(AEN_(2/3))*b(MN)*c(SiN_(4/3))*d ₁CeO_(3/2) *d ₂EuO*xSiO₂ *yAlO_(3/2)wherein AE is an alkaline earth metal chosen of the group of Ca, Mg, Srand Ba or mixtures thereof and M is a trivalent element chosen of thegroup of Al, B, Ga, Sc or mixtures thereofwith0.95≦2*(a+d1+d2)/(b+c+x+y)≦1.2a+d ₁ +d ₂ ≧c+x,(b+y):(c+x)≧1,(b+y)≦1+10*d ₁,b≧5*y,c≧10*x,0.0001≦d ₁≦0.2 and d1≧10*d2.

The term “essentially” means especially ≧95%, preferably ≧97% and mostpreferred ≧99% wt-%. However, in some applications, trace amounts ofadditives may also be present in the bulk compositions. These additivesparticularly include such species known to the art as fluxes. Suitablefluxes include alkaline earth—or alkaline—metal oxides, fluorides,SiONes, SiAlONes, SiO₂ and the like and mixtures thereof.

Such an illumination system has shown for a wide range of applicationswithin the present invention to have at least one of the followingadvantages:

-   -   The colour control of the illumination system can be greatly        enhanced due to the fact that for a wide range of applications        within the present invention changes in the blue wavelength of        the excitation source are compensated by spectral shift in the        conversion layer.    -   Overall very similar color points on the black body line of the        chromaticity diagram may be hit independent of the excitation        wavelength used for a wide range of applications within the        present invention.    -   The invented luminescent material shows excellent thermal and        photo-thermal stability of the luminescence efficiency, this in        combination with the above leads to a highly temperature stable        illumination system.    -   In addition, the invented luminescent material strongly absorbs        near UV to blue light over a wide spectral range, so it can be        used with various light sources.    -   A special property of the material is its capability to generate        a narrow range of color temperatures with different blue        emission wavelength, determined by the material composition.        According to a preferred embodiment of the present invention,        0.97≦2*(a+d1+d2)/(b+c+x+y)≦1.15, preferably,        1≦2*(a+d1+d2)/(b+c+x+y)≦1.10. This has been shown to lead to a        material with further improved lighting features for a wide        range of application within the present invention.

According to a preferred embodiment of the present invention, d1≧10*d2,preferably d1≧20*d2, more preferred d1≧30*d2 and most preferredd1≧40*d2.

This has been shown to lead to a material with further improved lightingfeatures for a wide range of application within the present invention.

According to a preferred embodiment of the present invention, the Ceriumdoping level d1 is ≧0.01% and ≦20% of a, i.e. the molar amount of thealkaline earth ion content (Ca, Mg, Sr and Ba).

According to a preferred embodiment of the present invention, theEuropium doping level d2 is ≧0.0001% and ≦2% of a, i.e. the molar amountof the alkaline earth ion content (Ca, Mg, Sr and Ba).

According to a preferred embodiment of the present invention, the fullwidth half maximum (FWHM) of the emission spectra of said at least oneluminescent material is ≧120 nm.

This has been shown to lead to a material with further improved lightingfeatures for a wide range of applications within the present invention.

Preferably, the half-width of the emission spectra of said at least oneluminescent material is ≧130 nm, more preferred ≧140 nm.

According to a preferred embodiment of the present invention, theemission spectrum of said at least one luminescent material shows acomposed emission band comprising at least one maximum in the wavelengthrange between ≧500 and ≦600 nm, preferably ≧530 and ≦570 and a fullwidth half maximum (FWHM) of ≧80 nm, preferably ≧100 and most preferred≧120 nm and a second emission maximum in the wavelength range between≧600 and ≦650 nm, preferably ≧600 and ≦620 nm and a full width halfmaximum (FWHM) of ≧30 and ≦140 nm, preferably ≦120 and most preferred≦100 nm.

This has been shown to lead to a material with further improved lightingfeatures for a wide range of applications within the present invention.

It goes without saying that the emission spectrum may be a superpositionof these two emissions (which will actually be the case for mostapplications within this embodiment of the present invention) andtherefore only one emission maximum may be observed. The two emissionsmay then be calculated by deconvolution.

According to a preferred embodiment of the present invention, afterexcitation with light emitting in the 400-480 nm spectral range, therelative emitted energy of the luminescent material in the 500-700 nmwavelength interval is ≧50%, more preferred ≧75%.

According to a preferred embodiment of the present invention, the ratio[M]:[Si], i.e. (b+y):(c+x), in said at least one luminescent material is≧1.01 and ≦1.20. By doing so it has been surprisingly found that the(photo-) thermal stability may for a wide range of applications withinthe present invention be increased even further.

Preferably the ratio [M]:[Si] in said at least one luminescent materialis ≧1.02 and ≦1.18, more preferred the ratio [M]:[Si] in said at leastone luminescent material is ≧1.03 and ≦1.15.

This has been shown to lead to a material with further improved lightingfeatures for a wide range of application within the present invention.

According to a preferred embodiment of the present invention (b+y) is≧2*d₁, more preferred (b+y) is ≧5*d₁. This has been shown to lead to amaterial with further improved lighting features for a wide range ofapplication within the present invention.

According to a preferred embodiment of the present invention, in said atleast one luminescent material b is ≧5*y, preferably b is ≧10*y, morepreferred b is ≧20*y. This has been shown to lead to a material withfurther improved lighting features for a wide range of applicationwithin the present invention.

According to a preferred embodiment of the present invention, in said atleast one luminescent material c is ≧10*x, more preferably c is ≧20*x,more preferred c is ≧50*y. This has been shown to lead to a materialwith further improved lighting features for a wide range of applicationwithin the present invention.

According to a preferred embodiment of the present invention, in said atleast one luminescent material d1 is ≦0.1. Preferably d1 is ≦0.03, morepreferred d₁ is ≦0.01.

According to a preferred embodiment of the present invention, in said atleast one luminescent material [Ba]+[Sr]+[Mg] is ≦0.9*[Ca], preferably[Ba]+[Sr]+[Mg] is ≦0.7*[Ca] and more preferred [Ba]+[Sr]+[Mg] is≦0.5*[Ca]. This has been shown to lead to a material with furtherimproved lighting features for a wide range of application within thepresent invention.

Preferably the at least one material is provided as powder and/or asceramic material.

If the at least one material is provided at least partially as a powder,it is especially preferred that the powder has a d₅₀ of ≧2 μm and ≦15μm. This has been shown to be advantageous for a wide range ofapplications within the present invention.

According to a preferred embodiment of the present invention, the atleast one material is at least partly provided as at least one ceramicmaterial.

The term “ceramic material” in the sense of the present invention meansand/or includes especially a crystalline or polycrystalline compactmaterial or composite material with a controlled amount of pores orwhich is pore free.

The term “polycrystalline material” in the sense of the presentinvention means and/or includes especially a material with a volumedensity larger than 90 percent of the main constituent, consisting ofmore than 80 percent of single crystal domains, with each domain beinglarger than 0.5 μm in diameter and having different crystallographicorientations. The single crystal domains may be connected by amorphousor glassy material or by additional crystalline constituents.

According to a preferred embodiment of the present invention, a lightemitting device especially a LED is provided comprising at least oneceramic material with an average diameter from ≧100 μm to ≦2000 μm, morepreferred ≧200 μm to ≦1500 μm, yet more preferred ≧250 μm to ≦1000 μmand most preferred ≧300 μm to ≦750 μm.

According to a preferred embodiment, the at least one ceramic materialhas a volume of ≧0.005 mm³ to ≦8 mm³, more preferred ≧0.03 mm³ to ≦1 mm³and most preferred ≧0.08 mm³ to ≦0.18 mm³.

According to a preferred embodiment, the at least one ceramic materialhas a density of ≧90% and ≦100% of the theoretical density. This hasbeen shown to be advantageous for a wide range of applications withinthe present invention since then the luminescent properties of the atleast one ceramic material may be increased.

More preferably the at least one ceramic material has a density of ≧97%and ≦100% of the theoretical density, yet more preferred ≧98% and ≦100%,even more preferred ≧98.5% and ≦100% and most preferred ≧99.0% and≦100%.

According to a preferred embodiment of the present invention, thesurface roughness RMS (disruption of the planarity of a surface;measured as the geometric mean of the difference between highest anddeepest surface features) of the surface(s) of the at least one ceramicmaterial is ≧0.001 μm and ≦1 μm.

According to an embodiment of the present invention, the surfaceroughness of the surface(s) of the at least one ceramic material is≧0.005 μm and ≦0.8 μm, according to an embodiment of the presentinvention ≧0.01 μm and ≦0.5 μm, according to an embodiment of thepresent invention ≧0.02 μm and ≦0.2 μm and according to an embodiment ofthe present invention ≧0.03 μm and ≦0.15 μm.

According to a preferred embodiment of the present invention, thespecific surface area of the at least one ceramic material is ≧10⁻⁷ m²/gand ≦0.1 m²/g.

A material and/or a light emitting device according to the presentinvention may be of use in a broad variety of systems and/orapplications, amongst them one or more of the following:

Office lighting systems

household application systems

shop lighting systems,

home lighting systems,

accent lighting systems,

spot lighting systems,

theater lighting systems,

fiber-optics application systems,

projection systems,

self-lit display systems,

pixelated display systems,

segmented display systems,

warning sign systems,

medical lighting application systems,

indicator sign systems, and

-   -   decorative lighting systems    -   portable systems    -   automotive applications    -   green house lighting systems

The aforementioned components, as well as the claimed components and thecomponents to be used in accordance with the invention in the describedembodiments, are not subject to any special exceptions with respect totheir size, shape, material selection and technical concept such thatthe selection criteria known in the pertinent field can be appliedwithout limitations.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional details, features, characteristics and advantages of theobject of the invention are disclosed in the subclaims, the figures andthe following description of the respective figures and examples,which—in an exemplary fashion—show several embodiments and examples of aluminescent material for use in an illumination system according to theinvention as well as several embodiments and examples of an illuminationsystem according to the invention.

FIG. 1 shows two emission spectra of two illumination system accordingto the present invention with LEDs emitting at different bluewavelengths combined with the luminescent material according to ExampleI of the present invention.

FIG. 2 shows CIE 1976 color coordinates of the two illumination systemsof FIG. 1 with different thickness plates of the luminescent ceramics.

FIG. 3 shows a zoom of FIG. 2 in the white region

FIG. 4 shows several emission spectra of further illumination systemsaccording to the present invention employing different thickness platesof the luminescent ceramics according to Example I of the presentinvention

FIG. 5 shows further several emission spectra of further illuminationssystems according to the present invention employing different thicknessplates of the luminescent ceramics according to Example I of the presentinvention

FIG. 6 shows a diagram of the x-y-color point coordinates against thetemperature of a luminescent material according to Example I of thepresent invention.

FIG. 7 shows a schematic diagram of illumination systems.

DETAILED DESCRIPTION OF EMBODIMENTS

The invention will be further understood by the following Example Iwhich—in a merely illustrative fashion—shows several materials of thepresent invention.

Example I

Example I refers to1.080(CaN_(2/3))*1.006(AlN)*0.963(SiN_(4/3))*0.0198CeO_(3/2)*0.0002EuO*0.018SiO₂*0.014AlO_(3/2)which was prepared in the following fashion:

All actions were carried out in dry inert gas atmosphere. 53.37 g Ca₃N₂(2N), 41.02 g AlN (3N), 0.78 g Al₂O₃, 45.30 g Si₃N₄, 1.09 g SiO₂, 3.41 gCeO₂ (4N) and 0.035 g Eu₂O₃ (4N) were intimately mixed by ball millingand the mixture was subsequently fired in forming gas atmosphere (N₂:H₂95:5 v/v) at 1500° C. maximum temperature. The obtained powder cake wasagain milled, granulated and pressed into pellets by uniaxial pressingand subsequent cold isostatic pressing until a green density of >50% wasreached. The pellets were sintered at 1650° C. in forming gasatmosphere, optionally this is followed by a hot isostatic pressing stepat 1 kbar N₂ to improve the density.

FIG. 7 shows a blue LED 1 and a blue LED 2 (=illuminations systems).Each of n-GaN layers 111A, 111B of LEDs 1, 2 are optically coupled bytransparent glue 112A, 112B with a refractive index of 1.5 (silicone) tothe luminescent ceramic plates 113A, 113B, which form the outer surfaces121A, 121B of the illumination, systems 1, 2. Besides the opticalfunctionality of the ceramic plates 113A, 113B they also form a rigidmechanical protection for the underlying roughened surfaces 120A, 120Bof n-GaN layers 111A, 111B of the LEDs.

FIG. 1 shows a white LED emission spectra with a luminescent ceramicplate made out of the material according to example I with 150 μmthickness on blue LED 1 with a dominant emission wavelength of 450 nmand blue LED 2 with a dominant emission wavelength of 464 nm. Asdescribed above the 1 mm² thin-film flip-chip InGaN—GaN LEDs 1, 2 areoptically coupled by a transparent glue 112A, 112B with a refractiveindex of 1.5 (silicone) to the luminescent ceramic plates 113A, 113B,which forms the outer surfaces 121A, 121B of the illumination systems.Besides the optical functionality of the ceramic plates 113A, 113B theyalso form a rigid mechanical protection for the underlying roughenedsurfaces 120A, 120B of n-GaN layers 111A, 111B of the LEDs.

It can be seen that the material according to Example I has a broad bandin the wavelength range of 500-700 nm leading to a warm-white emissionspectrum of the illumination systems with a correlated color temperature(CCT) between 3000 and 4000 K.

FIG. 2 shows the color points of the LEDs with luminescent ceramic plate(=illumination systems) of FIG. 1 together with the color points of theblue LEDs used in a CIE 1976 diagram.

FIG. 3 shows a zoomed view on the white region of FIG. 2. In this viewthe specific property of the luminescent material is visible tocounteract a variation of the blue LED emission. This property is verybeneficial for white LEDs in general illumination applications torealize a stable white emission color (stable CCT), even if the LEDemission spectrum undergoes changes due to variations in drive currentand junction temperature.

FIGS. 4 and 5 show emission spectra of selected white emitting LEDs withthe blue pumping LEDs, LED 1 for FIG. 4 and LED 2 for FIG. 5,respectively.

It can be shown that with the material according to Example I severalLEDs with low CCT and excellent colour rendering indices R_(a) and highcolour rendering index R₉ could be fabricated. R₉ is a measured for thereproduction of saturated red colours. The data are shown in Table I andII, whereby Table I refers to the spectra of FIG. 4 and Table II refersto the spectra of FIG. 5.

TABLE I CCT 4411 3583 3323 3286 3256 3231 3210 [K] Ra 82 76 73 73 73 7372 Δuv 0.025 0.006 0.004 0.006 0.007 0.008 0.009 x 0.3535 0.3942 0.42070.4251 0.4289 0.4323 0.4352 y 0.3116 0.3701 0.4081 0.4144 0.4199 0.42470.429 LE 273 307 327 330 333 335 337 [lm/W] R1 87.5 76.8 72.2 71.5 70.970.4 70 R2 86.1 81.2 78.1 77.6 77.2 76.9 76.6 R3 77.6 80.9 81.1 81.281.3 81.4 81.5 R4 81.7 75.5 73.8 73.5 73.3 73.1 73 R5 85.2 74.2 69.268.4 67.8 67.2 66.8 R6 75.7 70.7 66.6 66.1 65.6 65.1 64.8 R7 82.9 82.783.9 84.2 84.5 84.8 85.1 R8 81.2 67.9 63 62.3 61.7 61.2 60.8 R9 55.317.7 3.2 1 −0.7 −2.2 −3.5 R10 60.4 52 46.4 45.6 44.9 44.3 43.8 R11 78.369.8 67.1 66.7 66.3 66 65.7 R12 63.3 49.9 40.3 38.8 37.6 36.5 35.6 R1385.5 76.6 72 71.4 70.8 70.3 69.9 R14 85.6 88.2 88.6 88.7 88.7 88.8 88.9

TABLE II CCT 4587 3597 3395 3274 3230 3194 3163 3138 [K] Ra 89 81 79 7776 76 75 75 Δuv 0.021 0.006 0 0.003 0.005 0.006 0.007 0.008 x 0.35050.3942 0.4109 0.4228 0.4275 0.4316 0.4353 0.4385 y 0.3167 0.3716 0.39270.4076 0.4135 0.4187 0.4233 0.4273 LE 275 306 317 324 327 330 332 334[lm/W] R1 92.1 80.9 77.1 74.6 73.7 72.9 72.2 71.6 R2 94.8 89.4 85.9 83.682.7 81.9 81.3 80.7 R3 93.2 91.1 89.6 88.5 88.1 87.7 87.4 87.1 R4 83.175.7 73.9 72.8 72.3 72 71.6 71.4 R5 88.7 78.2 74.1 71.3 70.3 69.4 68.667.9 R6 85.9 80.6 76.5 73.5 72.4 71.4 70.6 69.8 R7 87.8 86.5 87 87.487.6 87.7 87.9 88.1 R8 84.7 69.5 65.8 63.5 62.6 61.8 61.2 60.7 R9 69.426.7 15.7 8.6 5.9 3.7 1.7 0.1 R10 87.9 69.6 62.6 57.9 56.2 54.7 53.452.3 R11 75.9 67.7 65.6 64.2 63.7 63.2 62.8 62.5 R12 65.6 55.8 48.4 42.940.7 38.8 37.2 35.6 R13 94.1 82.9 78.7 76 74.9 74.1 73.3 72.6 R14 95.994.3 93.3 92.7 92.5 92.3 92.1 92

FIG. 6 shows a diagram of the x-y-color coordinates (CIE 1931) againstthe temperature of a luminescent material according to Example I of thepresent invention. In this Figure it can be clearly seen that thex-y-color point stays nearly constant with temperature, which leads toan excellent color stability for a wide range of illumination systemsaccording to the present invention.

The particular combinations of elements and features in the abovedetailed embodiments are exemplary only; the interchanging andsubstitution of these teachings with other teachings in this and thepatents/applications incorporated by reference are also expresslycontemplated. As those skilled in the art will recognize, variations,modifications, and other implementations of what is described herein canoccur to those of ordinary skill in the art without departing from thespirit and the scope of the invention as claimed. Accordingly, theforegoing description is by way of example only and is not intended aslimiting. The invention's scope is defined in the following claims andthe equivalents thereto. Furthermore, reference signs used in thedescription and claims do not limit the scope of the invention asclaimed.

The invention claimed is:
 1. A luminescent material comprising:(AEN_(2/3))*b(MN)*c(SiN_(4/3))*d₁CeO_(3/2)*d₂EuO*xSiO₂*yAlO_(3/2)wherein AE is an alkaline earth metal chosen from a group consisting ofCa, Mg, Sr and Ba or mixtures thereof and M is a trivalent elementchosen from a group consisting of Al, B, Ga, Sc or mixtures thereof,wherein0.95≦2*(a+d ₁ +d ₂)/(b+c+x+y)≦1.2a+d ₁ +d ₂ ≧c+x,(b+y):(c+x)≧1,(b+y)≦1+10*d ₁,b≧5*y,c≧10*x,0.0001≦d ₁≦0.2 and d ₁≧10*d ₂; wherein the surface roughness of at leastone surface of the luminescent material, measured as the geometric meanof the difference between highest and deepest surface features is ≧0.001μm and ≦1 μm.
 2. The luminescent material of claim 1 wherein theluminescent material is a ceramic.
 3. The luminescent material of claim1 wherein the luminescent material is ≧95%(AEN_(2/3))*b(MN)*c(SiN_(4/3))*d₁CeO_(3/2)*d₂EuO*xSiO₂*yAlO_(3/2). 4.The luminescent material of claim 1 further comprising at least oneflux.
 5. The luminescent material of claim 4 wherein the at least oneflux comprises an alkaline material.
 6. The luminescent material ofclaim 4 wherein the at least one flux comprises one of a metal oxide anda fluoride.
 7. The luminescent material of claim 4 wherein the at leastone flux comprises one of SiON, SiAlON, and SiO₂.
 8. The luminescentmaterial of claim 1 wherein (b+y):(c+x) is ≧1.01 and ≦1.20.
 9. Theluminescent material of claim 1 wherein (b+y) is ≦1+10*d₁.
 10. Theluminescent material of claim 1 wherein b≧5*y and c≧10*x.
 11. A devicecomprising: a blue LED; and a ceramic plate attached to the blue LED,the ceramic plate comprising a luminescent material, the luminescentmaterial comprising(AEN_(2/3))*b(MN)*c(SiN_(4/3))*d₁CeO_(3/2)*d₂EuO*xSiO₂*yAlO_(3/2)wherein AE is an alkaline earth metal chosen from a group consisting ofCa, Mg, Sr and Ba or mixtures thereof and M is a trivalent elementchosen from a group consisting of Al, B, Ga, Sc or mixtures thereof,wherein0.9≦2*(a+d ₁ +d ₂)/(b+c+x+y)≦1.2a+d ₁ +d ₂ ≧c+x,(b+y):(c+x)≧1,(b+y)≦1+10*d ₁,b≧5*y,c≧10*x,0.0001≦d ₁≦0.2 and d ₁≧10*d ₂ wherein the light output of the device hasa Δuv≦0.025, 72≦Ra≦89 and 273≦LE≦337.
 12. The device of claim 11 whereinthe n-GaN layer is optically coupled to the ceramic plate by atransparent glue.
 13. The device of claim 12 wherein the transparentglue is silicone.
 14. The device of claim 12 wherein the transparentglue has an index of 1.5.
 15. The device of claim 11 wherein a surfaceof the blue LED facing the ceramic plate is roughened.
 16. The device ofclaim 15 wherein the ceramic plate forms a rigid mechanical protectionfor the blue LED.
 17. The device of claim 15 wherein the surfaceroughness of at least one surface of the ceramic plate, measured as thegeometric mean of the difference between highest and deepest surfacefeatures is ≧0.001 μm and ≦1 μm.
 18. The device of claim 11 wherein afull width half maximum of an emission spectrum of the luminescentmaterial is ≧120 nm.
 19. The device of claim 11 wherein the emissionspectrum of the luminescent material comprises: an emission maximum in awavelength range between 500 and 600 nm having a full width half maximumof ≧80 nm; and an emission maximum in a wavelength range between 600 and650 nm having a full width half maximum of ≧30 and ≦140 nm.
 20. Thedevice of claim 11 wherein combined light comprising light emitted bythe blue LED and light emitted by the luminescent material has acorrelated color temperature between 3000 and 4000 K.